And there's the heart of the problem.
When I worked there 30 years ago, Boeing equipment was designed and largely built by Boeing personnel.
Boeing management, in its infinite wisdom, has decided that design, testing and manufacturing can be "subbed out", with major components assembled like tinker toys. The brilliance of their MBAs (Master Bullshit Artists) is clearly visible in the 787.
When we built the prototype wings for the 767 (in Everett, Washington), they broke at 115% of the design breaking load. My group designed a good part of the tooling. But then we built stuff to work, not to be the lowest cost bidder.
In-house gives you control (and responsibility) for all phases of the design and manufacturing process. But it can be pretty expensive as all that specialized design and manufacturing expertise has to be kept busy and that can be difficult.
Subcontracting the work out allows the prime contractor to reduce in-house investment in staff and equipment. With proper design reviews, quality control measures, warranties, etc. good quality parts that meet design requirements can be produced. In addition, in comparison to the in-house staff, a subcontractor specializing in a particular functional area or component... say, hydraulic pumps...can develop a much greater depth of expertise through successful completing many more projects.
Aye, but there's the rub. Depending overmuch on that subcontracted expertise can lead to complacency. The subcontractor may begin to think that all jobs are simply variations on a common theme. The prime contractor may begin to put too much confidence in the subcontractor's expertise. In this case, GS Yuasa is a sub to a sub, Thales. So you may have two levels of relying on someone else’s expertise at play here (Boeing to Thales, Thales to GS Yuasa).
If, as Jazusamo posted, the issue comes down to the specific type of lithium battery selected (lithium cobalt oxide), it is going to be very interesting to see who made the recommendation to adopt that battery type and what kind of development and certification testing was done on the batteries and their control circuits.